1. Field of the Invention
The invention relates to an electric heating device for motor vehicles. In particular, the invention relates to an electric heating device provided with a heating register which comprises separately controllable heating zones.
2. Description of the Related Art
In motor vehicles, and in particular in motor vehicles with consumption-optimized internal combustion engines, electric heating devices are used for heating the vehicle interior and the engine. Such electric heating devices are, however, also suitable to be used for room air conditioning, for industrial plants, household appliances, etc.
The improved efficiency of consumption-optimized internal combustion engines causes a substantial reduction of the heating power in motor vehicles. When the engine operates in the lower partial-load range and when outside temperatures are low, e.g. in winter, the engine does not supply the amount of heat required for heating the vehicle interior. For compensating such a shortage of heat, auxiliary electric heatings are used, which are normally integrated in air conditioning units of motor vehicles.
A multi-zone air conditioning of the vehicle interior allows every passenger (driver, front passenger, and back-seat passengers) to adjust the temperature individually and independently. Additional discharge means direct the air onto the windows of the vehicle for defrosting.
Such multi-zone air conditioning, in the case of which each passenger can adjust the temperature prevailing at his seat separately, is nowadays realized with the aid of water heat exchangers. The percentage of hot air for the air current of each zone can be dosed via a flap control. Conventional electric heating devices (auxiliary heatings) are used for heating the air current in its entirety, i.e. without making a difference between the individual air subcurrents, if the water heat exchanger should fail to provide a sufficient amount of heat.
These conventional auxiliary electric heatings and vehicle air conditioning units are disadvantageous insofar as an individual supply of heat to the respective “zones” cannot be effected separately. An adequate air conditioning for each zone is e.g. only realizable via a suitable flap control (mixing flaps for hot air/cold air) for dosing the amount of heat supplied to each zone. It follows that, when non-uniform amounts of heat are demanded in the individual air conditioning zones of the vehicle, a high percentage of the electric energy is needlessly converted into power, and a fine adjustment of the heating power adapted to each air conditioning zone is not possible, especially not in the case of auxiliary electric heatings having a particularly high heating power (e.g. 2 kW).